114 INTEIINAL MOUTHrATJTS. 



downwards so as to constitute a cone, with the outer mouth-parts 

 on the end (Fig. 16) : this cone is evidently somewhat longer in 

 Stomoxys than in Glossina. Fig. 12 represents the median part 

 of the posterior side of the head and the labium (e) in Glossina, 

 with the long membrane (d) between both ; c is the occipital 

 foramen, a the firmly chitinised part. It will be seen that there 

 is a deep median incision, which is membranous, and surrounded 

 at the sides by the firm chitiu which borders the eyes below ; the 

 labium can be pulled upwards, so that its basal part occupies this 

 median area, the membrane being invaginated and folded. On 

 the fi'ont side of the head the epistoma, which is the median area 

 below the transverse prominence under the antennae, is mem- 

 branous in Glossina, with the exception of an upper ti'ansverse 

 area, which is coalesced with the wings of the pharynx (see 

 below). In Stomoxys the epistoma shows essentially the same 

 structure, but the sul)-basal transverse solid chitin is short, and 

 from it two parallel dark strips run downwards (Fig. lG,i) nearly 

 to the base of the maxillary palpi. The muscles which effect the 

 protrusion and retraction of the membranous cone are mentioned 

 below. The maxillai-y palpi (Fig. 16, g) are inserted on the 

 anterior side of the cone, a little below its upper margin. No 

 other vestige of the maxillae and no rudiment of mandibles can 

 be discovered ; but in Sfomoxi/s I found at the base of each palpus 

 a very small curved chitinous strip (Fig. 16, h), movably united 

 with the palpus. Whether this strip is a rudiment of the maxilla 

 I cannot say. 



E. The Internal Moutii-parts op Glamna and Stomoxys, and 

 THEIR Mode op Action. 



From the tube constituted by the extei'nal mouth-parts the 

 blood is conducted into the pharynx, which is a vei-y large and 

 complicated organ. In the natural position and seen from the 

 side (Fig. 21) it is nearly vertical, but slopes slightly forwards. 

 It is obliquely triangular, with the two upper posterior lateral 

 angles produced into a moderately short {Glossina, Fig. 2, m) or a 

 very long process (Stomoxys, Fig, 21) ; in Stomoxys the two upper 

 anterior angles are also produced. Fig. 13 represents the pharynx 

 of Glossina seen from behind, together with the basal part of the 

 oesophagus [d), and a small anterior separate part (c) between 

 the pharynx itself and the external mouth-parts. F'ig. 14 is a 

 diagrammatic section of the same pharynx at its thickest point : 



